Charged particle beam apparatuses are used in a plurality of industrial fields. Testing of semiconductor devices during manufacturing, exposure systems for lithography, detecting devices and inspection systems are only some of these fields.
In general, there is a high demand for structuring and inspecting specimens within the micrometer or nanometer scale. On such a small scale, process control, inspection or structuring is often done with charged particle beams, e.g. electron beams, which are generated and focused in charged particle beam devices such as electron microscopes or electron beam pattern generators. Charged particle beams offer superior spatial resolution compared to, e.g. photon beams due to their short wavelengths.
However, for a given beam diameter, the charged particle beam current limits the throughput of charged particle beam systems. Since further miniaturization of, e.g. structures to be imaged is necessary, the charged particle beam diameter has to be decreased. As a result, the beam current for individual beams and thus, the throughput has to be decreased.
In order to increase the total charged particle beam current and thus, the throughput, a plurality of charged particle beams can be used. One option for a system applying a plurality of charged particle beams is to combine several single beam columns with each other. However, some of the components, especially magnetic lenses, cannot be miniaturized sufficiently. Thus, the columns have to be spaced such that the electron beams have a distance of 100 mm to 200 mm.
U.S. Pat. No. 3,715,580 shows a multi-electron beam recorder having a new type of magnetic electron lens, whereby a common excitation coil excites a plurality of closely spaced through holes in a circular pole piece. Thereby, due to the common excitation coil, two electron beams can be focused more closely together as compared to the minimal distance of two separate beam columns.
A further multi-beam device is shown in U.S. patent Publication US2001/0028038 A1. Therein, a magnetic lens for a plurality of electron beams is shown. A plurality of lens openings within a pole piece area share one excitation coil.
However, such systems can lack uniformity of the focusing properties with respect to the individual lenses provided by each lens opening. This lack of uniformity is intended to be solved by U.S. patent Publication US2001/0028038 A1 due to lens intensity beam adjusters.
Such a state of the art optic for focusing a plurality of electron beams is shown in FIG. 20. The magnetic lens 200 can be used to focus a plurality of electron beams. The optical axes of the lens are denoted with reference signs 201. The upper pole piece 202 and lower pole piece 203 guide magnetic fields to the openings 204. Within each opening 204 one electron beam is focused. The openings 204 are arranged e.g. in a matrix within the circular pole pieces. Coil 205 provides a magnetic field when excited. Due to the arrangement of the magnetic lens 200, the magnetic field influencing the individual electron beams varies from one opening to the other. The prior art lens intends to compensate for these inhomogeneous focusing properties and further inhomogeneous focusing properties due to manufacturing tolerances. This is intended to be achieved by lens intensity adjuster 206. The lens intensity adjuster 206 accelerates or decelerates the respective electron beam locally within the area of the lens intensity adjuster, thereby compensating for the inhomogeneous field strength of the magnetic lens 200 with respect to the individual openings 204.
Since there is a strong requirement for improving resolution and for minimizing aberrations in such systems, it is an object of the present invention to further improve state of the art devices.